1. Field of Invention
This invention relates to corrosion resistant alloys, particularly to corrosion resistant alloys in which chromium is the predominant element and more particularly to such an alloy structure useful as a weld depositable hard-facing on a mechanical face seal in contact with sea water. Applications for relative motion while being subjected to sea water require alloys that are highly resistant to sea water corrosion especially in the presence of accelerating factors such as galvanic effects. A submarine propeller shaft and a seal on underwater oil drilling apparatus are two examples of such uses.
2. Description of Prior Art
Prior seals, in the case of submarine shaft seals, have used a hard-facing, wear resistant alloy on a carrier ring, more particularly a cobalt containing weld deposited overlay on a Monel ring as the mating wear face. Unfortunately, the severe corrosion which occurs at the Monel-overlay interface threatens the integrity of the mating face. One solution for this corrosion problem is to use an insert of the hard-facing alloy electrically isolated and mechanically bonded into a machined groove in the Monel mating ring. The weld overlay type of construction at the weld interface is more desirable because it results in a more stable sealing face. An example of a corrosion resistant weld-deposited hard-facing alloy of the weld overlay type above is recorded in Vreeland, et al., "Development of Materials Resistant to Wear and Corrosion for Mechanical Face Seal Applications", David Taylor Naval Ship Research and Development Center Report 4299 (November 1974), herein incorporated by reference and cited as prior art by applicant. The composition disclosed therein is defined to consist of the following elements by weight percent: 2.9-3.1%-C, 42.5-45.5-Cr, 2.1-2.4-Cb, 6.9-7.2-Mo, 2.1-2.4-Fe, 0.6-0.75-Si, and 39.7-43.7-Ni. Another example of a hard-facing alloy that indicates good corrosion and wear properties under shaft seal conditions is a proprietary alloy known as Haynes Alloy N-6. The exacting proportions of this alloy are not publically known.
There is a continuing need for a hard-facing alloy material of known composition that provides improved resistance to sea water corrosion, especially in the presence of a galvanic environment.